In Harvard historian Henry Louis Gates Jr.'s telling, Black Christianity is not a monolith but a mosaic of many faiths and denominations, flavored by African traditions and customs; and yet the institution itself is a kind of majestic fortress. His vibrant, incisive "The Black Church," a companion book to the new PBS series, leads us along hidden corridors as it unearths revelatory stories while pounding the pulpit with passionate arguments about faith and justice.

To contemplate religion in America is to contemplate the Black/white divide. Tens of thousands of Africans who survived the Middle Passage were Muslim; Gates delves into the subtle ways Islam shaped early African American Christianity. Slaves first gathered covertly in praise houses, away from the ambivalent gaze of their white owners, who sought to control them with parables of a meek, submissive Jesus while shunning the liberation narrative of Exodus.

After Appomattox, "The Black Church, in a society in which the color line was strictly policed, amounted to a world within the world," Gates writes. "[It] was the proving ground for the nourishment and training of a class of leaders; it fostered community bonds and established the first local, regional, and then national Black social networks."

The mother continent beget its own rituals of songs and dance. "The vocals, the melodies, the repetitions, the ring shout — all were as distinct from white American music and worship as Black people were from white people," Gates observes. "Musicians and singers used repetition as a basis for improvisation, like a jazz soloist breaking away from the beat."

With a surgeon's skill, Gates teases out the threads of the various Black denominations — Baptist, African Methodist Episcopal and Church of Christ, among them — and their dogmatic skirmishes. His is a charismatic cast, from the titans — Sojourner Truth, Martin Luther King Jr. and Jesse Jackson — to lesser-known figures, such as Richard Harvey Cain, Jarena Lee and Vashti Murphy McKenzie, all profiles in courage.

Gates is particularly strong as he portrays the complex battles of women as they fought for authority, and the sexism that dogged them each step of the way. He also doesn't shy away from Black Christianity's homophobia.

Meticulously reported, the book is its own rich sermon. Gates is proselytizing us, and it's nigh impossible to not stamp our feet and shout, "Amen!" Interestingly, he neglects to explore how the white religious right studied the Black Church's strategies and tactics; the rise of the dogmatic Moral Majority in the 1980s was a kind of racial call-and-response to the "good trouble" of civil-rights-era pastors.

Through a glass darkly, Jerry Falwell Sr. and Pat Robertson had learned from Rev. King and even Malcolm X, forging the politicized white evangelicalism, the Black Church's doppelgänger, that plagues us today.

And yet "The Black Church" is a marvel, a breezy, illuminating tale of a distinctly powerful institution at the beating heart of the American Experiment, and an invaluable work from a masterful chronicler.

Hamilton Cain is the author of "This Boy's Faith: Notes From a Southern Baptist Upbringing" and a member of the National Book Critics Circle. He lives in Brooklyn.

The Black Church
By: Henry Louis Gates Jr.
Publisher: Penguin Press, 304 pages, $30.